1. Field of the Invention
The present invention relates to a magnetic tape device, and more particularly to a magnetic tape device comprising a tape guide, which is suitable for the high-speed travel of a magnetic tape.
2. Description of the Related Art
A magnetic tape device utilizes a magnetic tape, which is a tape-shaped magnetic recording medium, makes the magnetic tape travel while being guided by rotating tape guides (roller guides), and reads/writes data by using a magnetic head in relation to the magnetic tape thereof.
A magnetic tape is guided within a tape travel path by a plurality of tape guides. This magnetic tape is housed in a tape cartridge. The magnetic tape is wound around a file reel disposed inside the cartridge. The cartridge is introduced into the inside of a magnetic tape device by a loader. The magnetic tape housed inside the cartridge is attached to a machine reel by having the end thereof guided by a threader. The machine reel takes up the magnetic tape wound around the file reel.
FIG. 8 is a block diagram showing one example of the placement of tape guides and a magnetic head, which constitute a magnetic tape device. In FIG. 8, tape guides 1L, 1R are lined up in the direction of travel of the magnetic tape and positioned on a base 3. A magnetic head 2 is affixed on the base 3 between tape guides 1L and 1R. Magnetic head 2 can perform data read/write by arbitrarily selecting any one of a plurality of tracks (for example, 24). That is, there is provided a plurality of playback head portions 2a and recording head portions 2b for each track.
FIG. 9 is a cross-sectional view showing one example of a conventional tape guide. In FIG. 9, a tape guide 1 comprises a fixed shaft 10. This fixed shaft 10 is affixed to a base 3. Two bearings 11, 11xe2x80x2 support a rotating shaft 12 rotatably around fixed shaft 10. This rotating shaft 12 is a so-called cylindrical roller. The peripheral surface 12a of this roller 12 is a guide surface for guiding a magnetic tape. Peripheral surface 12a of roller 12 guides a magnetic tape in a state in which same makes contact with the recording surface of the magnetic tape. Roller 12 rotates in accordance with the frictional force between the magnetic tape and roller 12 when the magnetic tape travels. The rotational speed of peripheral surface 12a of roller 12 becomes the same as the travel speed of the magnetic tape. A lower flange 13 is affixed to the bottom side of fixed shaft 10. An upper flange 14 is disposed on the top side of fixed shaft 10. Upper flange 14 comprises a movable portion 14b, a fixed portion 14a and a coil spring 15. Fixed portion 14a is affixed to a small diameter portion 10a of fixed shaft 10. Movable portion 14b is fitted onto the small diameter portion 10a so as to be capable of moving up and down along the small diameter portion 10a. Coil spring 15 biases movable portion 14b toward a step portion 16 of fixed shaft 10. The force by which coil spring 15 biases movable portion 14b constitutes a force for biasing a magnetic tape to lower flange 13. Movable portion 14b is capable of moving up and down along the small diameter portion 10a of fixed shaft 10. Movable portion 14b, under the biasing force of coil spring 15, is hit against step portion 16 of fixed shaft 10. Applying suitable biasing force in accordance with coil spring 15 enables a magnetic tape to be made to travel along lower flange 13. Because a magnetic tape will not be biased to lower flange 13 if the biasing force is too weak, a magnetic tape will slip out of position in the up-down direction of the roller guide during tape travel. Slippage causes uneven winding on the take-up reel, and becomes a cause of the edges of a magnetic tape folding. Further, if the biasing force is too strong, there is the danger of the edges of a magnetic tape being either folded or scraped, and of a magnetic tape being destroyed.
In a magnetic tape device of this kind, in order for magnetic tape read/write processing to be carried out faster, it is necessary for a magnetic tape to be made to travel at higher speed.
However, the problem is that a conventional tape guide (roller guide) has low endurance to highspeed rotation, and the life of a conventional tape guide decreases when it is rotated at high speed.
Meanwhile, a hydrobearing guide is well-known as a tape guide for use in place of a roller guide, which rotates in accordance with the travel of a magnetic tape. A hydrobearing guide is constituted from, for example, a ceramic, and because it does not rotate in accordance with magnetic tape travel, has high durability. The peripheral surface of a hydrobearing guide has a circular arc surface for guiding a magnetic tape along the tape travel path, and it is known that when a magnetic tape is made to travel at high speed, the magnetic tape travels by levitating without coming into contact with the circular arc surface. The following expression is known as an expression for approximating the degree of levitation of a magnetic tape.
Degree of levitation expression
hxe2x88x920.643r(6xcexcV/T)⅔
h: degree of levitation, r: radius of curvature of guide, xcexc: viscosity of air, V: tape travel velocity, T: tape tension
By making a magnetic tape travel by levitating in relation to a tape guide, the magnetic tape does not come in contact with the circular arc surface, thus enabling the prevention of magnetic tape friction during highspeed travel. Based on the above expression, the larger the circular arc radius of the circular arc surface (the radius of curvature r of the above-mentioned expression) at this time, the greater the degree of levitation of a magnetic tape in relation to the circular arc surface. Therefore, to ensure the required degree of levitation, it is necessary that the circular arc that forms the tape travel path be set to a predetermined radius.
However, when a magnetic tape is being wound onto the take-up reel, or in the interval until a stopped magnetic tape achieves highspeed travel, and furthermore, in the interval until a magnetic tape travelling at high speed is stopped, the magnetic tape travels by making contact with the circular arc surface (According to the above-mentioned expression, the degree of levitation is proportional to the tape travel speed, and when the tape travel speed is slow, a magnetic tape is not levitated.) To curb as much as possible the friction of a magnetic tape resulting from the magnetic tape traveling by making contact with the circular arc surface, it is necessary to improve as much as possible the relative surface roughness of the circular arc surface of a hydrobearing guide.
However, the problem is that, when the relative surface roughness of the circular arc surface is improved, when a magnetic tape comes in contact with the circular arc surface, the magnetic tape sticks to the circular arc surface. When an attempt is made to make a magnetic tape travel after the magnetic tape has been stuck to the circular arc surface one time, the magnetic tape either breaks or stretches, causing the magnetic tape to be damaged.
The sticking of a magnetic tape tends to occur more readily the larger the contact surface area of the magnetic tape and circular arc surface. To make the contact surface area smaller, it is necessary to make the circular arc radius of the circular arc surface smaller, but by so doing, as explained hereinabove, it becomes impossible to make a magnetic tape travel so that it levitates at a sufficient degree of levitation.
Therefore, an object of the present invention is to provide a magnetic tape device, which is capable of making a magnetic tape travel stably without being stuck to a hydrobearing guide.
A magnetic tape device of the present invention comprises a magnetic head for performing read/write operation to a magnetic tape traveling a tape travel path, and tape guides, each of which has a guide surface for guiding the magnetic tape along the tape travel path, and which are positioned respectively on the upstream side and downstream side of the magnetic head, wherein the guide surface of the tape guide is formed by a plurality of circular arc surfaces.
For example, the tape guide may have a flange for forming a reference travel position for one edge in the width direction of the magnetic tape, and a flat spring for biasing the other edge of the magnetic tape to the travel reference position.
Further, the flat spring has an elongated portion having a prescribed length, and a protruding portion which is formed on the end that is opposite to the fixed end of the elongated portion, and the protruding portion comes in contact with the magnetic tape. The elongated portion may have a tapering shape toward from the fixed end to the opposite end. The flat spring is preferably provided in the same number as the plurality of circular arc surfaces, and each flat spring biases the magnetic tape on each circular arc surface.